1. Field of the Invention
The present invention relates to a fuel injection control system for an in-cylinder direct injection, spark-ignition internal combustion engine employing a fuel injection valve or a fuel injector in which fuel is injected directly into the combustion chamber of each engine cylinder, and specifically to technologies of improving the engine's startability and ensuring good starting performance in in-cylinder fuel direct injection, spark-ignition internal combustion engines.
2. Description of the Prior Art
In conventional in-cylinder fuel direct injection, spark-ignition engines, during cold-engine start, the injector pulse width for engine starting is set and also a proper fuel injection timing is achieved, depending on at least the engine coolant temperature. One such conventional fuel injection controller for an in-cylinder fuel direct injection, spark-ignition engine has been disclosed in Japanese Patent Provisional Publication No. 8-193536. The prior-art fuel injection controller of a fuel direct injection, spark-ignition engine, as disclosed in the Japanese Patent Provisional Publication No. 8-193536, is generally designed in such a manner as to inject or spray fuel into the engine cylinders until the controller identifies or discriminates an engine cylinder. That is to say, in one sequential fuel-injection method such as port fuel injection of injecting fuel into the intake-air passageway upstream of the intake valve port, during the engine starting period, it is possible to enhance or improve the engine's startability by simultaneous injection of fuel into each of the engine cylinders before the engine-cylinder identification or discrimination is completed. On the contrast, in the other sequential fuel-injection method such as fuel direct injection of injecting fuel directly into the combustion chamber of each engine cylinder, there is a problem that the fuel injected into the working engine cylinder being on the exhaust stroke is exhausted through the exhaust port and a lot of unburned fuel vapors pass through the exhaust system, assuming that the previously-noted simultaneous fuel injection with respect to all of the engine cylinders is made before the engine-cylinder identification is completed. For the reasons discussed above, in fuel direct injection, spark-ignition engines, fuel injection is usually initiated after the engine-cylinder identification is completed. However, when exceeding a usual or normal fuel injection timing (based on at least a crank angle) for a first engine cylinder being on its intake stroke at the time when the engine-cylinder identification has been completed, the first fuel injection is initiated at a usual fuel injection timing for a second engine cylinder coming up on its intake stroke subsequently to the first engine cylinder and then the second engine cylinder is spark-ignited, thus retarding the initial explosion in the combustion chamber by two ignition actions during the engine cranking and starting period. This deteriorates the engine's startability.